背景にも描画してみる。きちんと、背景に描画されるわけじゃないのね。描画された順か。

        private void button1_Click(object sender, EventArgs e)
        {
            Pen pen1 = new Pen(Color.Black);
            Brush brush1 = new SolidBrush(Color.Red);
            Graphics g1 = Graphics.FromImage(pictureBox1.Image);
            g1.FillEllipse(brush1, 15, 15, 100, 150);
            g1.DrawEllipse(pen1, 10, 10, 140, 150);
            g1.DrawEllipse(pen1, 10, 20, 200, 200);

            Pen pen2 = new Pen(Color.Magenta, 5);
            Brush brush2 = new SolidBrush(Color.Chocolate);
            Graphics g2 = Graphics.FromImage(pictureBox1.BackgroundImage);
            g2.FillEllipse(brush2, 10, 10, 300, 300);
            g2.DrawEllipse(pen2, 0, 0, 150, 130);
            g2.DrawLine(pen2, 0, 0, 200, 200);

            pictureBox1.Refresh();
        }

先に描画しておけば、問題なしですな